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PCE Working Group                                                H. Chen
Internet-Draft                                                  D. Dhody
Intended status: Standards Track                     Huawei Technologies
Expires: October 31, 2018                                 April 29, 2018


       A Forward-Search P2P TE LSP Inter-Domain Path Computation
         draft-chen-pce-forward-search-p2p-path-computation-15

Abstract

   This document presents a forward search procedure for computing paths
   for Point-to-Point (P2P) Traffic Engineering (TE) Label Switched
   Paths (LSPs) crossing a number of domains using multiple Path
   Computation Elements (PCEs).  In addition, extensions to the Path
   Computation Element Communication Protocol (PCEP) for supporting the
   forward search procedure are described.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on October 31, 2018.

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   include Simplified BSD License text as described in Section 4.e of




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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Conventions Used in This Document . . . . . . . . . . . . . .   4
   4.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .   4
   5.  Forward Search Path Computation . . . . . . . . . . . . . . .   5
     5.1.  Overview of Procedure . . . . . . . . . . . . . . . . . .   5
     5.2.  Description of Procedure  . . . . . . . . . . . . . . . .   5
     5.3.  Processing Request and Reply Messages . . . . . . . . . .   8
   6.  Comparing to BRPC . . . . . . . . . . . . . . . . . . . . . .   9
   7.  Extensions to PCEP  . . . . . . . . . . . . . . . . . . . . .   9
     7.1.  RP Object Extension . . . . . . . . . . . . . . . . . . .   9
     7.2.  NODE-FLAGS Object . . . . . . . . . . . . . . . . . . . .  10
       7.2.1.  PREVIOUS-NODE TLV . . . . . . . . . . . . . . . . . .  11
       7.2.2.  DOMAIN-ID TLV . . . . . . . . . . . . . . . . . . . .  11
       7.2.3.  PCE-ID TLV  . . . . . . . . . . . . . . . . . . . . .  12
     7.3.  Candidate Node List . . . . . . . . . . . . . . . . . . .  13
     7.4.  Result Path List  . . . . . . . . . . . . . . . . . . . .  14
     7.5.  Request Message Extension . . . . . . . . . . . . . . . .  14
     7.6.  Reply Message Extension . . . . . . . . . . . . . . . . .  15
   8.  Suggestion to improve performance . . . . . . . . . . . . . .  15
   9.  Manageability Considerations  . . . . . . . . . . . . . . . .  15
     9.1.  Control of Function and Policy  . . . . . . . . . . . . .  15
     9.2.  Information and Data Models . . . . . . . . . . . . . . .  15
     9.3.  Liveness Detection and Monitoring . . . . . . . . . . . .  15
     9.4.  Verify Correct Operations . . . . . . . . . . . . . . . .  15
     9.5.  Requirements On Other Protocols . . . . . . . . . . . . .  16
     9.6.  Impact On Network Operations  . . . . . . . . . . . . . .  16
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  16
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  16
     11.1.  Request Parameter Bit Flags  . . . . . . . . . . . . . .  16
     11.2.  New PCEP Object  . . . . . . . . . . . . . . . . . . . .  16
       11.2.1.  NODE-FLAGS Object  . . . . . . . . . . . . . . . . .  16
     11.3.  New PCEP TLV . . . . . . . . . . . . . . . . . . . . . .  17
       11.3.1.  DOMAIN-ID TLV  . . . . . . . . . . . . . . . . . . .  17
   12. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . .  17
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  18
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  18
     13.2.  Informative References . . . . . . . . . . . . . . . . .  18
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  19







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1.  Introduction

   It would be useful to extend MPLS TE capabilities across multiple
   domains (i.e., IGP areas or Autonomous Systems) to support inter-
   domain resources optimization, to provide strict QoS guarantees
   between two edge routers located within distinct domains.

   [RFC4105] "Requirements for Inter-Area MPLS TE" lists the
   requirements for computing a shortest path for a TE LSP crossing
   multiple IGP areas; and [RFC4216] "MPLS Inter-Autonomous System (AS)
   TE Requirements" describes the requirements for computing a shortest
   path for a TE LSP crossing multiple ASes.  [RFC4655] "A PCE-Based
   Architecture" discusses centralized and distributed computation
   models for the computation of a path for a TE LSP crossing multiple
   domains.

   This document presents a forward search procedure to address these
   requirements using multiple Path Computation Elements (PCEs).  This
   procedure guarantees that the path found from the source to the
   destination is shortest.  It does not depend on any sequence of
   domains from the source node to the destination node.  Navigating a
   mesh of domains is simple and efficient.

2.  Terminology

   The following terminology is used in this document.

   ABR:  Area Border Router.  Router used to connect two IGP areas
      (Areas in OSPF or levels in IS-IS).

   ASBR:  Autonomous System Border Router.  Router used to connect
      together ASes of the same or different service providers via one
      or more inter-AS links.

   BN:  Boundary Node.  A boundary node is either an ABR in the context
      of inter-area Traffic Engineering or an ASBR in the context of
      inter-AS Traffic Engineering.

   Entry BN of domain(n):  a BN connecting domain(n-1) to domain(n)
      along the path found from the source node to the BN, where
      domain(n-1) is the previous hop domain of domain(n).

   Exit BN of domain(n):  a BN connecting domain(n) to domain(n+1) along
      the path found from the source node to the BN, where domain(n+1)
      is the next hop domain of domain(n).

   Inter-area TE LSP:  a TE LSP that crosses an IGP area boundary.




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   Inter-AS TE LSP:  a TE LSP that crosses an AS boundary.

   LSP:  Label Switched Path

   LSR:  Label Switching Router

   PCC:  Path Computation Client.  Any client application requesting a
      path computation to be performed by a Path Computation Element.

   PCE:  Path Computation Element.  An entity (component, application,
      or network node) that is capable of computing a network path or
      route based on a network graph and applying computational
      constraints.

   PCE(i):  a PCE with the scope of domain(i).

   TED:  Traffic Engineering Database.

   This document uses terminology defined in [RFC5440].

3.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

4.  Requirements

   This section summarizes the requirements specific for computing a
   path for a P2P Traffic Engineering (TE) LSP crossing multiple domains
   (areas or ASes).  More requirements for Inter-Area and Inter-AS MPLS
   Traffic Engineering are described in [RFC4105] and [RFC4216].

   A number of requirements specific for a solution to compute a path
   for a P2P TE LSP crossing multiple domains is listed as follows:

   1.  The solution SHOULD provide the capability to compute a shortest
       path dynamically, satisfying a set of specified constraints
       across multiple IGP areas.

   2.  The solution MUST provide the ability to reoptimize in a
       minimally disruptive manner (make before break) an inter-area TE
       LSP, should a more optimal path appear in any traversed IGP area.

   3.  The solution SHOULD provide mechanism(s) to compute a shortest
       end-to-end path for a TE LSP crossing multiple ASes and
       satisfying a set of specified constraints dynamically.




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   4.  Once an inter-AS TE LSP has been established, and should there be
       any resource or other changes inside anyone of the ASes, the
       solution MUST be able to re-optimize the LSP accordingly and non-
       disruptively, either upon expiration of a configurable timer or
       upon being triggered by a network event or a manual request at
       the TE tunnel Head-End.

5.  Forward Search Path Computation

   This section gives an overview of the forward search path computation
   procedure (FSPC for short) to satisfy the requirements described
   above and describes the procedure in detail.

5.1.  Overview of Procedure

   Simply speaking, the idea of FSPC for computing a path for an MPLS TE
   P2P LSP crossing multiple domains from a source node to a destination
   node includes:

   Start from the source node and the source domain.

   Consider the optimal path segment from the source node to every exit
   boundary node of the source domain as a special link;

   Consider the optimal path segment from an entry boundary node to
   every exit boundary node and the destination node of a domain as a
   special link; and the optimal path segment is computed as needed.

   The whole topology consisting of many domains can be considered as a
   special topology, which contains those special links and the inter-
   domain links.

   Compute an optimal path in this special topology from the source node
   to the destination node using CSPF.

5.2.  Description of Procedure

   Suppose that we have the following variables:

   A current PCE named as CurrentPCE which is currently computing the
   path.

   A candidate node list named as CandidateNodeList, which contains the
   nodes to each of which the temporary optimal path from the source
   node is currently found and satisfies a set of given constraints.
   The information about each node C in CandidateNodeList consists of:

   o  the cost of the path from the source node to node C,



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   o  the hopcount of the path from the source node to node C,

   o  the previous hop node P and the link between P and C,

   o  the domain list of C (ABR or ASBR) where C has visibility to
      multiple domains and clearly mark the domain by which C is added
      to CandidateNodeList,

   o  the PCE responsible for C (i.e., the PCE responsible for the
      domain containing C.  Alternatively, we may use the above
      mentioned domain instead of the PCE.), and

   o  the flags for C.

   The flags include:

   o  bit D indicating that C is a Destination node if it is set,

   o  bit S indicating that C is the Source node if it is set,

   o  bit T indicating that C is on result path Tree if it is set.

   The nodes in CandidateNodeList are ordered by path cost.  Initially,
   CandidateNodeList contains only a Source Node, with path cost 0, PCE
   responsible for the source domain.

   A result path list or tree named as ResultPathTree, which contains
   the final optimal paths from the source node to the boundary nodes or
   the destination node.  Initially, ResultPathTree is empty.

   Alternatively, the result path list or tree can be combined into the
   CandidateNodeList.  We may set bit T to one in the NODE-FLAGS object
   for the candidate node when grafting it into the existing result path
   list or tree.  Thus all the candidate nodes with bit T set to one in
   the CandidateNodeList constitute the result path tree or list.

   FSPC for computing the path for the MPLS TE P2P LSP is described as
   follows:

   Initially, a PCC sets ResultPathTree to empty and CandidateNodeList
   to contain the source node and sends PCE responsible for the source
   domain a PCReq with the source node, the destination node,
   CandidateNodeList and ResultPathTree.

   When the PCE responsible for a domain (called current domain)
   receives a request for computing the path for the MPLS TE P2P LSP, it
   obtains node Cm with the minimum path cost in the CandidateNodeList.
   The node Cm is the first node in the CandidateNodeList, which is



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   sorted by path cost.  It checks whether the CurrentPCE is the PCE
   responsible for the node Cm(always expand node Cm only if it is an
   entry boundary node).  If it is, then remove Cm from
   CandidateNodeList and graft it into ResultPathTree (i.e., set flag
   bit T of node Cm to one); otherwise, a PCReq message is sent to the
   PCE for node Cm (see Section 5.3 for the case that there is not any
   direct session between the CurrentPCE and the PCE for node Cm).

   Suppose that node Cm is in the current domain.  The ResultPathTree is
   built from Cm in the following steps.

   If node Cm is the destination node, then the optimal path from the
   source node to the destination node is found, and a PCRep message
   with the path is sent to the PCE/PCC which sends the request to the
   CurrentPCE.

   If node Cm is an entry boundary node or the source node, then the
   optimal path segments from node Cm to the destination node (if it is
   in the current domain) and every exit boundary node of the current
   domain that is not on the result path tree and satisfies the given
   constraints are computed through using CSPF and as special links.

   For every node N connected to node Cm through a special link (i.e.,
   the optimal path segment satisfying the given constraints), it is
   merged into CandidateNodeList.  The cost to node N is the sum of the
   cost to node Cm and the cost of the special link (i.e., the path
   segment) between Cm and N.  If node N is not in the
   CandidateNodeList, then node N is added into the list with the cost
   to node N, node Cm as its previous hop node and the PCE for node N.
   The PCE for node N is the CurrentPCE if node N is an ASBR; otherwise
   (node N is an ABR, an exit boundary node of the current domain and an
   entry boundary node of the domain next to the current domain) the PCE
   for node N is the PCE for the next domain.  If node N is in the
   CandidateNodeList and the cost to node N through node Cm is less than
   the cost to node N in the list, then replace the cost to node N in
   the list with the cost to node N through node Cm and the previous hop
   to node N in the list with node Cm.

   If node Cm is an exit boundary node and there are inter-domain links
   connecting to it (i.e., node Cm is an ASBR) and satisfying the
   constraints, then for every node N connecting to Cm, satisfying the
   constraints and not on the result path tree, it is merged into the
   CandidateNodeList.  The cost to node N is the sum of the cost to node
   Cm and the cost of the link between Cm and N.  If node N is not in
   the CandidateNodeList, then node N is added into the list with the
   cost to node N, node Cm as its previous hop node and the PCE for node
   N.  If node N is in the CandidateNodeList and the cost to node N
   through node Cm is less than the cost to node N in the list, then



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   replace the cost to node N in the list with the cost to node N
   through node Cm and the previous hop to node N in the list with node
   Cm.

   After the CandidateNodeList is updated, there will be a new node Cm
   with the minimum cost in the updated CandidateNodeList.  If the
   CurrentPCE is the same as the PCE for the new node Cm, then the node
   Cm is removed from the CandidateNodeList and grafted to
   ResultPathTree (i.e., set flag bit T of node Cm to one), and the
   above steps are repeated; otherwise, a request message is to be sent
   to the PCE for node Cm.

   Note that if node Cm has visibility to multiple domains, do not
   remove it from the CandidateNodeList until it is expanded in all
   domains.  Also mark in the domain list of node Cm, for which domains
   it is already expanded.

5.3.  Processing Request and Reply Messages

   In this section, we describe the processing of the request and reply
   messages with Forward search bit set for FSPC.  Each of the request
   and reply messages mentioned below has its Forward search bit set
   even though we do not indicate this explicitly.

   In the case that a reply message is a final reply, which contains the
   optimal path from the source to the destination, the reply message is
   sent toward the PCC along the path that the request message goes from
   the PCC to the current PCE in reverse direction.

   In the case that a request message is to be sent to the PCE for node
   Cm with the minimum cost in the CandidateNodeList and there is a PCE
   session between the current domain and the next domain containing
   node Cm, the CurrentPCE sends the PCE for node Cm through the session
   a request message with the source node, the destination node,
   CandidateNodeList and ResultPathTree.

   In the case that a request message is to be sent to the PCE for node
   Cm and there is not any PCE session between the CurrentPCE and the
   PCE for node Cm, a request message with T bit set to one in RP is
   sent toward a branch point on the result path tree from the current
   domain along the path that the request message goes from the PCC to
   the CurrentPCE in reverse direction.  From the branch point, there is
   a downward path to the domain containing the previous hop node of
   node Cm on the result path tree and to the domain containing node Cm.
   At this branch point, the request message with T bit set to zero is
   sent to the PCE for node Cm along the downward path.





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6.  Comparing to BRPC

   [RFC5441] describes the Backward Recursive Path Computation (BRPC)
   algorithm or procedure for computing an MPLS TE P2P LSP path from a
   source node to a destination node crossing multiple domains.
   Comparing to BRPC, there are a number of differences between BRPC and
   the Forward-Search P2P TE LSP Inter-Domain Path Computation (FSPC).
   Some of the differences are briefed below.

   First, for BRPC to compute a shortest path from a source node to a
   destination node crossing multiple domains, we MUST provide a
   sequence of domains from the source node to the destination node to
   BRPC in advance.  It is a big burden and very challenging for users
   to provide a sequence of domains for every LSP path crossing domains
   in general.  In addition, it increases the cost of operation and
   maintenance of the network.  FSPC does not need any sequence of
   domains for computing a shortest path.

   Secondly, for a given sequence of domains domain(1), domain(2), ...
   ,domain(n), BRPC searches the shortest path from domain(n), to
   domain(n-1), until domain(1) along the reverse order of the given
   sequence of domain.  It will get the shortest path within the given
   domain sesuence.  FSPC calculates an optimal path in a special
   topology from the source node to the destination node.  It will find
   the shortest path within all the domains.

   Moreover, if the sequence of domains from the source node to the
   destination node provided to BRPC does not contain the shortest path
   from the source to the destination, then the path computed by BRPC is
   not optimal.  FSPC guarantees that the path found is optimal.

7.  Extensions to PCEP

   This section describes the extensions to PCEP for FSPC.  The
   extensions include the definition of a new flag in the RP object, a
   result path list and a candidate node list in the PCReq and PCRep
   message.

7.1.  RP Object Extension

   The following flags are added into the RP Object:

   The F bit is added in the flag bits field of the RP object to tell
   the receiver of the message that the request/reply is for FSPC.

          o F (FSPC bit - 1 bit):
              0: This indicates that this is not a PCReq/PCRep for FSPC.
              1: This indicates that this is a PCReq or PCRep for FSPC.



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   The T bit is added in the flag bits field of the RP object to tell
   the receiver of the message that the request is for transferring a
   request message to the domain containing the node with minimum cost
   in the candidate list.

          o T (Transfer request bit - 1 bit):
              0: This indicates that this is not a PCReq
                 for transferring a request message.
              1: This indicates that this is a PCReq message
                 for transferring a request message.

   Setting Transfer request T-bit in a RP Object to one indicates that a
   reqest message containing the RP Object is for transferring a request
   message to the domain containing the node with minimum cost in the
   candidate list.

   The IANA request is referenced in Section below (Request Parameter
   Bit Flags) of this document.

   This F bit with the N bit defined in [RFC6006] can indicate whether
   the request/reply is for FSPC of an MPLS TE P2P LSP or an MPLS TE
   P2MP LSP.

          o F = 1 and N = 0: This indicates that this is a PCReq/PCRep
                             message for FSPC of an MPLS TE P2P LSP.
          o F = 1 and N = 1: This indicates that this is a PCReq/PCRep
                             message for FSPC of an MPLS TE P2MP LSP.

7.2.  NODE-FLAGS Object

   The NODE-FLAGS object is used to indicate the characteristics of the
   node in a Candidate Node List in a request or reply message for FSPC.
   The NODE-FLAGS object comprises a Reserved field, and a number of
   Flags.  The NODE-FLAGS object may also contain a set of TLVs.

   The format of the NODE-FLAGS object body is as follows:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |D|S|T|              Flags      |         Reserved              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       ~                      Optional TLVs                            ~
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                          NODE-FLAGS Object Body




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   where

   o  D = 1: The node is a destination node.

   o  S = 1: The node is a source node.

   o  T = 1: The node is on the result path tree.

   Following are the TLVs defined to convey the characteristics of the
   candidate node.

7.2.1.  PREVIOUS-NODE TLV

   The PREVIOUS-NODE TLV contains the Previous Node Id of the candidate
   node.  The PREVIOUS-NODE TLV has the following format:

          0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     address-type              |          Reserved             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       ~                      Previous Node Id                         ~
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                         PREVIOUS-NODE TLV format

   The Type of PREVIOUS-NODE TLV is to be assigned by IANA.

   The length is 8 if the address type is IPv4 or 20 if the address type
   is IPV6.

   Address Type (16 bits): Indicates the address type of Previous Node
   Id. 1 means IPv4 address type, 2 means IPv6 address type.

   Reserved(16 bits): SHOULD be set to zero on transmission and MUST be
   ignored on receipt.

   Previous Node Id : IP address of the node.

7.2.2.  DOMAIN-ID TLV

   The DOMAIN-ID TLV contains the domain Id of the candidate node (ABR
   or ASBR).  The NODE-FLAG Object may include multiple DOMAIN-ID TLVs
   when the candidate node has visibility into multiple Domains.

   The DOMAIN-ID TLV has the following format:




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          0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |       Domain Type             |         Flags             |C|V|
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                       Domain ID                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                           DOMAIN-ID TLV format

   The Type of DOMAIN-ID TLV is to be assigned by IANA.

   The length is 8.

   Domain Type (8 bits): Indicates the domain type.  There are two types
   of domain defined currently:

   o  Type=1: the Domain ID field carries an IGP Area ID.

   o  Type=2: the Domain ID field carries an AS number.

   C Flag (1 bit): If the flag is set to 1, it indicates the candidate
   node is added into Candidate Node List by this domain.

   V Flag (1 bit): If the flag is set to 1, it indicates the candidate
   node has been expanded in this domain.

   Domain ID (32 bits): With the Domain Type set to 1, this indicates
   the 32-bit Area ID of an IGP area where the candidate belongs.  With
   Domain Type set to 2, this indicates an AS number of an AS where the
   candidate belongs.  When the AS number is coded in two octets, the AS
   Number field MUST have its first two octets set to 0.

   [Editor's note: [PCE-HIERARCHY-EXT], section 3.1.3 deals with the
   encoding of Domain-Id TLV in OPEN Object.  Later on DOMAIN-ID TLV
   defined here can be incorporate with this draft]

7.2.3.  PCE-ID TLV

   The PCE-ID TLV is used to indicate the PCE that added this node to
   the CandidateList.  The PCE-ID TLV has the following format:










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        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |           Address Type        |            Reserved           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       ~                     PCE IP Address                            ~
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                             PCE-ID TLV format

   The type of PCE-ID TLV is to be assigned by IANA.

   The length is 8.

   Address Type (16 bits): Indicates the address type of PCE IP Address.
   1 means IPv4 address type, 2 means IPv6 address type.

   PCE IP Address: Indicates the reachable address of a PCE.

   [Editor's note: [PCE-HIERARCHY-EXT], section 3.1.4 deals with the
   encoding of PCE-Id TLV in OPEN Object.  Later on PCE-ID TLV defined
   here can be incorporate with this draft]

7.3.  Candidate Node List

   The Candidate Node List has the following format:


            <candidate-node-list>::= <node>
                                     [<candidate-node-list>]
            where

            <node>::= <ERO>  <NODE-FLAGS>
                      <attribute-list>

            <attribute-list>::=<metric-list>
                               [<IRO>]

            <metric-list>::=<METRIC>[<metric-list>]


   The ERO in a candidate node contain just the path segment of the last
   link of the path, which is from the previous hop node of the tail end
   node of the path to the tail end node.  With this information, we can
   graft the candidate node into the existing result path list or tree.





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   Simply speaking, a candidate node has the same or similar format of a
   path defined in [RFC5440], but the ERO in the candidate node just
   contain the tail end node of the path and its previous hop, and the
   candidate path may contain a new object NODE-FLAGS along with new
   TLVs.

7.4.  Result Path List

   The Result Path List has the following format:


            <result-path-list>::= <node>
                                  [<result-path-list>]
            where

            <node>::= <ERO>  <NODE-FLAGS>
                      <attribute-list>

            <attribute-list>::=<metric-list>
                               [<IRO>]

            <metric-list>::=<METRIC>[<metric-list>]


   The usage of ERO, NODE-FLAGS objects etc, is similar to Candidate
   Node List.  The T-bit of NODE-FLAGS Object would be set denoting that
   the best path to this node is already found.

7.5.  Request Message Extension

   Below is the message format for a request message with the extension
   of result-path-list and candidate-node-list:

            <PCReq Message>::= <Common Header>
                               [<svec-list>]
                               <request-list>

            <request-list>::=<request>[<request-list>]

            <request>::= <RP> <END-POINTS> [<OF>] [<LSPA>] [<BANDWIDTH>]
                         [<metric-list>]  [<RRO>[<BANDWIDTH>]]  [<IRO>]
                         [<LOAD-BALANCING>]
                         [<result-path-list>]
                         [<candidate-node-list>]
         where:
                         <result-path-list> and <candidate-node-list>
                         are as defined above.




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7.6.  Reply Message Extension

   Below is the message format for a reply message with the extension of
   result-path-list and candidate-node-list:


              <PCRep Message> ::= <Common Header>
                                 <response-list>

              <response-list> ::=<response>[<response-list>]

              <response> ::= <RP> [<NO-PATH>] [<attribute-list>]
                             [<path-list>]
                             [<result-path-list>]
                             [<candidate-node-list >]
           where:
                           <result-path-list> and <candidate-node-list>
                           are as defined above.

   If the path from the source to the destination is found, the reply
   message contains path-list comprising the information of the path.

8.  Suggestion to improve performance

   To get much better performance all the candidate nodes of current
   domain can be expanded before moving on to a new domain.  Note in
   this case, after expanding the least cost candidate node, PCE can
   look for and expand any other candidates in this domain.

9.  Manageability Considerations

9.1.  Control of Function and Policy

   TBD

9.2.  Information and Data Models

   TBD

9.3.  Liveness Detection and Monitoring

   TBD

9.4.  Verify Correct Operations

   TBD





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9.5.  Requirements On Other Protocols

   TBD

9.6.  Impact On Network Operations

   TBD

10.  Security Considerations

   The mechanism described in this document does not raise any new
   security issues for the PCEP protocols.

11.  IANA Considerations

   This section specifies requests for IANA allocation.

11.1.  Request Parameter Bit Flags

   Two new RP Object Flags have been defined in this document.  IANA is
   requested to make the following allocation from the "PCEP RP Object
   Flag Field" Sub-Registry:

            Bit       Description                         Reference
            TBA       FSPC                     (F-bit)    This I-D
            TBA       Transfer Request         (T-bit)    This I-D

   Setting FSPC F-bit in a RP Object to one indicates that a request/
   reply message containing the RP Object is for FSPC.

   Setting Transfer Request T-bit in a RP Object to one indicates that a
   request message containing the RP Object is for transferring a
   request message to the domain containing the node with minimum cost
   in the candidate list.

11.2.  New PCEP Object

11.2.1.  NODE-FLAGS Object

   The NODE-FLAGS Object-Type and Object-Class has been defined in this
   document.  IANA is requested to make the following allocation:

   NODE-FLAGS Object-Type : TBA

   NODE-FLAGS Object-Class: TBA

   Flag field of the NODE-FLAG Object:




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            Bit      Description                           Reference
              0      The node is a destination node        This I-D
              1      The node is a source node             This I-D
              2      The node is on the result path tree   This I-D

   Each bit should be tracked with the following qualities:

   o  Bit number (counting from bit 0 as the most significant bit)

   o  Name flag

   o  Reference

11.3.  New PCEP TLV

   IANA is requested to make the following allocation:

            Value         Meaning                    Reference
              TBA         DOMAIN-ID TLV              This I-D
              TBA         PCE-ID TLV                 This I-D
              TBA         PREVIOUS-NODE TLV          This I-D

11.3.1.  DOMAIN-ID TLV

   IANA is requested to make the following allocation:

   Flag field of the DOMAIN-ID TLV

            Bit  Name    Description                           Reference
             15  V-bit   Candidate Node has been expanded by   This I-D
                         the domain
             14  C-bit   Candidate Node added by the domain    This I-D

   Each bit should be tracked with the following qualities:

   o  Bit number (counting from bit 0 as the most significant bit)

   o  Name flag

   o  Reference

12.  Acknowledgement

   The authors would like to thank Julien Meuric, Daniel King, Ramon
   Casellas, Cyril Margaria,Olivier Dugeon, Oscar Gonzalez de Dios,
   Udayasree Palle, Reeja Paul and Sandeep Kumar Boina for their
   valuable comments on this draft.




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13.  References

13.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC4655]  Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
              Element (PCE)-Based Architecture", RFC 4655,
              DOI 10.17487/RFC4655, August 2006,
              <https://www.rfc-editor.org/info/rfc4655>.

   [RFC5440]  Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol (PCEP)", RFC 5440,
              DOI 10.17487/RFC5440, March 2009,
              <https://www.rfc-editor.org/info/rfc5440>.

13.2.  Informative References

   [RFC4105]  Le Roux, J., Ed., Vasseur, J., Ed., and J. Boyle, Ed.,
              "Requirements for Inter-Area MPLS Traffic Engineering",
              RFC 4105, DOI 10.17487/RFC4105, June 2005,
              <https://www.rfc-editor.org/info/rfc4105>.

   [RFC4216]  Zhang, R., Ed. and J. Vasseur, Ed., "MPLS Inter-Autonomous
              System (AS) Traffic Engineering (TE) Requirements",
              RFC 4216, DOI 10.17487/RFC4216, November 2005,
              <https://www.rfc-editor.org/info/rfc4216>.

   [RFC5441]  Vasseur, JP., Ed., Zhang, R., Bitar, N., and JL. Le Roux,
              "A Backward-Recursive PCE-Based Computation (BRPC)
              Procedure to Compute Shortest Constrained Inter-Domain
              Traffic Engineering Label Switched Paths", RFC 5441,
              DOI 10.17487/RFC5441, April 2009,
              <https://www.rfc-editor.org/info/rfc5441>.

   [RFC6006]  Zhao, Q., Ed., King, D., Ed., Verhaeghe, F., Takeda, T.,
              Ali, Z., and J. Meuric, "Extensions to the Path
              Computation Element Communication Protocol (PCEP) for
              Point-to-Multipoint Traffic Engineering Label Switched
              Paths", RFC 6006, DOI 10.17487/RFC6006, September 2010,
              <https://www.rfc-editor.org/info/rfc6006>.







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   [PCE-HIERARCHY-EXT]
              Zhang, F., Zhao, Q., King, O., Casellas, R., and D. King,
              "Extensions to Path Computation Element Communication
              Protocol (PCEP) for Hierarchical Path Computation Elements
              (PCE) (draft-zhang-pce-hierarchy-extensions-02)", August
              2012.

Authors' Addresses

   Huaimo Chen
   Huawei Technologies
   Boston, MA
   USA

   EMail: Huaimo.chen@huawei.com


   Dhruv Dhody
   Huawei Technologies
   Leela Palace
   Bangalore, Karnataka  560008
   INDIA

   EMail: dhruv.dhody@huawei.com



























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